Bleaching fiber pulp



Patented a. 22, 1929 UNITED STATES PATENT orricl-z KORATIO A. HELDEB, OF CANTON, NORTH CAROLINA, ASSIGNOR TO THE CHAMPION FIBRE COMPANY, OF CANTON,

NOBEL? CAROLINA, A CORPORATION OF OHIO BLEACHING FIBER PULP No Drawing.

This invention relates to a process of lid is concerned with an improvement in a ess of bleaching wood pulp.

It heretofore has been known in the art that, in the process of bleaching fiber pulp, for example, wood pulp,-the speed of bleaching, and removal of the products of the bleaching treatment by washing with water, can be greatlyfacilitated by slightly procacidifying the fiber prior to the conclusion of the bleaching operation. It a has been known, also, that the rate and character of the bleaching treatment are determined to some extent by the suitable adjustment and maintenance of the hydrogen ion concentration of the water suspension of the fiber pulp during the treatment: for example, too low a'hydrogen ion concentration may result in an excessive increase in the time re uired to complete the bleaching action. A avorable degree of acidity is that represented by pH values between 4.0 and 3.0.

I have found that the bleaching of fiber pulp by means of commonly used bleaching agents, such as, for example, a solution of bleaching powder, and the removal of the products thereof, may be facilitated by the addition to the fiber pulp of an aqueous liquid obtained as condensate from the evaporation concentration of dilute tannin extract, which aqueous liquid is known in the art as sweet water. i

In the extraction of tannic acid and other tannins from wood and/or wood bark,-for example, from the bark or/and woody parts of the American chestnut t-ree,by means of hot water, there are extracted at the same time other water-soluble organic compounds which are,-with relation to tannic acid,relatively volatile. The resulting aqueous extract is relatively dilute and'requires concentration in order to obtain a commercially useful extract of high tannin content. In general practice, the concentration is effected by-evaporation,-usually, by vacuum distillation by means of multiple effect evaporators. I During the concentration operation there are volatilized water and at least a part of thesaid volatile, water-soluble,

Application filed June 15,

1928. Serial ms. 285,782.

organic compounds extracted from the wood or bark. Upon condensation, there is obtained the aqueous acidic condensate, known as sweet water,-the use of which in p the bleaching of fiber pulp forms the basis of the present invention. This aqueous acidic condensate heretofore has been a waste material causing difficulty in its disposal.

I have found that the aqueous condensates obtained from the evaporation concentration of dilute tannin extracts have an acid reaction equivalent in acidity to approximately 0.006 normal, and may have a pH value of 3.8,-i. e., within the range 4.0 to 3.0 hereinbefore described as representing favorable acidities of the wash waters and/or pulp.

I have found that the addition of the abovedescribed aqueous acidic liquid obtained as.

condensate rpm the evaporation concentration of tannin extract to the unbleached pulp or to the pulp undergoing bleaching treatment results in a more rapid bleaching and in an economy of bleach.

The substitution thereof for a dilute acid in the known bleaching processes efl'ects an improvement in the quality of the resulting bleached pulp and aneconomy of bleach. and as well opens up a field of usefulness for this hitherto-considered waste material.

The sweet water may be added to the pulp in such manner as to displace the residual water in a pulpwhich has been thickened to a consistency of about 8% or more; or, it may be added atthe conclusion of the bleaching treatment and prior to washing;

or, in order that the sweet water may have ample opportunity to penetrate the pulp fibers, it may be added to the partially in a single stage or in succes bleached pul sive stages chiringthe period of bleaching. l have discovered that. by the use of this sweet water. the bleach residues are readily removed and that a pulp of superior whitcacidity of the sweet water may, if desired, be adjusted as onthe one hand by dilution or on the other hand by addition thereto of I a regulated small amount of acid;

I claim:

1. In processes of bleaching fiber pulp, the step which consists in the addition to the pulp at any stage prior to the removal of v bleachresidues therefrom by water washing of an aqueous condensate from the evaporation concentration of an aqueous tannin extract. 7 I

2. In. processes of bleaching fiber pulp, the

step which consists in the addition to the til pulp at any stage prior to the removal of bleach residues therefrom by water washing of an aqueous condensate from the evaporation concentration of an aqueous tannin ex; tract, said condensate having an acidity falling within the range of pH values of 4.0 to 3.0. a

3. In processes of bleaching fiber pulp, the step which consists in the, addition to the pulp prior to the bleaching treatment of an aqueous condensate from the evaporation concentration of an aqueous tannin extract.

4. In processes of bleaching fiber pulp, the step which consists in the addition to the pulp prior to the bleaching treatment of an aqueous condensate from the evaporation concentration of an aqueous tannin extract, said condensate having an acidity falling within the range of pH values of 4.0 to 3.0.

In testimony whereof. I afiix mv signature.

HORATIO A. HELDER. 

